Spawners in Mineshaft ( maybe in dungeons also ) do not turn when you had load the chunk in Gamemode 3 . If you come to the spawner in GM 3 and then you do your gamemode 0 near from the spawner and you do your gamemode 3 again, the spawner has a bug when you look at it.
Yeah, the little mob inside is shaking alot instead of standing still as it should when you're in spectator mode.